Non-union is an arrest in the fracture repair process. There is progressive evidence of non-healing of a fracture of a bone. It is generally defined as a failure to reach bony union by 6 months postinjury.

Generally, disuse osteoporosis presents as a diffuse osteopenia seen throughout the disused body part. However, other patterns of osteopenia may also be noted. Lucent bands of osteopenia may be seen just proximal to the physeal line.

Another common pattern is a subchondral distribution to the osteopenia. This subchondral lucency is especially common in the bones of the foot and ankle following trauma. This pattern can even be a helpful prognostic sign in some cases, such as fractures of the talar neck. Fractures in this location frequently disrupt the blood supply to the proximal talar fragment, which may lead to post-traumatic osteonecrosis. However, the presence of subchondral osteopenia in such a fracture is a good prognostic sign, since one cannot develop disuse osteopenia without an intact blood supply to that bone. This is sometimes referred to as the “Hunter-Hawkins sign” or simply “Hawkins sign”.